The present invention relates to LED based lighting systems, in particular lighting systems comprising a large amount of LED units, each LED unit comprising one or more LEDs. Such lighting systems can e.g. be applied to display images on walls of buildings or provide in a light show on such a wall.
In general, the output characteristics of the large amount of LED units are controlled by connecting the LED units to a control unit via a network. As an example, the lighting system can comprise one or more groups of LED units in a daisy chain arrangement, whereby control signals are provided to the LED units using the DMX protocol, whereby the LED units are e.g. connected to each other via a RS-485 multi master bus.
When such a lighting system is in operation and e.g. provided to a wall of a tall building, it may be difficult to detect the malfunctioning of one or more of the LED units or at least to assess exactly which of the LED units is malfunctioning. Further, even if such detection were feasible, a quick repair of a malfunctioning LED unit is such a system would be difficult and time consuming. As such, the availability of the lighting system can be compromised at times.
Further, with respect to the application of differential lines like the RS-485 communication bus over comparatively large distances, it has been observed that such systems may be susceptible to EMI (electromagnetic interference). In order to avoid such EMI issues, it is often proposed to use so-called pull-up or pull-down resistances and to use a shielded communication line. Such solutions however result in an increased cost for the system or increase the overall power consumption of the system.